It is known that molting of arthropods, including insects and crustaceans, is induced by several types of ecdysteroids having molting hormone activity.
At least two uses have been developed for these molting hormones.
One of these is the application thereof to growth control, including acceleration of the timing of molting or metamorphosis of individuals and equalization of pupation. This enables, for example, silk thread production in silkworms to be controlled.
The other use is the application thereof to a gene expression system in a cultured cell line, a transgenic animal, or a transgenic plant, the system enabling a high level of expression of a target gene and control of expression timing to be obtained by a molting hormone treatment. This is based on the finding that the molting hormone binds to a molting hormone receptor, which is a transcription factor, and further binds to a molting hormone responsive element on a molting hormone responsive gene, thus controlling the transcription activity of the responsive gene.
For example, a molting hormone receptor and a target gene having a molting hormone responsive element incorporated into its transcription control region are first introduced into these systems, and the intracellular molting hormone concentration is increased by using a method such as addition to a cultured cell line (Christopherson, K. S. et al. (1992) Proc. Natl. Acad. Sci. USA 89, 6314–6318), injection into an animal (No, D et al. (1996) Proc. Natl. Acad. Sci. USA 93, 3346–3351), or absorption via a plant root (Martinez, A. et al. (1999) The Plant Journal 19, 97–106), thus inducing expression of a target gene product. Among these methods, one employing a cultured cell line has already been put into practice as a kit.
On the other hand, a technique for enhancing the activity of the molting hormone without using the molting hormone itself has also been developed. For example, examples thereof include the application to insect pest control of an ecdysteroid having a high molting hormone activity, and a more stable and strong molting hormone agonist having no ecdysteroid skeleton.
In this way, techniques for increasing molting hormone activity have already been developed.
In contrast, hardly any techniques for decreasing molting hormone activity, that is, techniques for inactivating the molting hormone present within a body or cells, have been developed.
A baculovirus-derived ecdysteroid UDP-glucosyltransferase gene (JP, A, 11-123079) has recently been receiving attention as a gene of an enzyme having an ability to inactivate the molting hormone. However, since there are defects such as it being necessary for UDP-glucose to be present at the same time in order for the enzyme to function, it has not yet been put into practice as a purified enzyme preparation or a recombinant protein.